Sum difference transducer shading

ABSTRACT

A torpedo homing system providing wide angle steering information from a directional transducer sum and difference signals. A transducer having columns of pick-up elements arranged in quadrants to provide the sum and difference signals wherein a portion of the windings normally designated for the elements of each quadrant are wound on some of the elements in the adjacent quadrants to extend the region of correct torpedo steering.

ueller et -al.'

SUM DIFFERENCE TRANSDUCER SHADING Inventors: William J. Mue1ler,Portsmouth; Frank W. Cuomo, East Providence, both of RI.

Assignee: The United States of America as represented by the Secretaryof the Navy Filed: Jan. 27, 1966 Appl. No.: 523,459

US. Cl ..340/6 R, 114/23, 340/6 5,

340/1 1 Int. Cl. ..G01s 3/80 Field of Search ...340/6 R, 6 S, 8 R,

[ 1 Apr. 24, 1973 [56] References Cited UNITED STATES PATENTS 3,025,4933/1962 Brooks ..340/6 3,082,401 3/1963 Bland et a1. ....340/11 3,160,84812/1964 Rey, Jr. et a1. ..340/6 Primary Examiner-Richard A. FarleyAttorney-J. P. Dunlavey and J. O. Tresansky [57] ABSTRACT A torpedohoming system providing wide angle steering information from adirectional transducer sum and difference signals. A transducer havingcolumns of pick-up elements arranged in quadrants to provide the sum anddifference signals wherein a portion of the windings normally designatedfor the elements of each quadrant are wound on some of the elements inthe adjacent quadrants to extend the region of correct torpedo steering.

5 Claims, 13 Drawing Figures Sheets-Sheei 5 BRIDGE OUTPUT VOLTAG ES Fly.60

VS. 30 BEARING (TARGETANGLE DIAGONAL PLANE 5 BRIDGE OUTPUT VOLTAGES vs.3o BEARING (TARGET ANGLE) INVENTORS WILL/AM J. MUELLER FRANK W. GUOMO BYATTORNEY AGE/VT Patented A ril 24, 1973 Y 3,129,703

5 Sheets-Sheet 4 F/g. 7b 8 4o RECEIVING PATTERN AAAAAAAAAAA NE 1 j#vvmroks W/LL/AM J. MUELLER FRA/KK W. G'UOMO AGE/VT Patented April 24,1973 BIO 5 Sheets-Sheet 5 Fig.8

STEERING SIGNAL VS. TARGET ANGLE PHASE SH IFTER lNVE/VTORS WILL/AM J.MUELLER FRANK W. GUOMO E) I ATTzZ/VEY AGE/VT SUMMER 1 SUM DIFFERENCETRANSDUCER SHADIN G The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

This invention relates to a signal processing system employingunderwater directional transducers and more particularly to a processingsystem and method of providing wide angle steering information fromtransducer sum and difference signals.

In torpedo homing systems of the type contemplated, steering informationis obtained by taking the sun and difference of signals from the leftand right halves of a transducer for a target in the horizontal planeand from the top and bottom halves for a target in the vertical plane.Sound reflected from a target impinging upon one-half of the transducerbefore the other provides an indication that the target is not centered.After appropriate comparisons of the sum and difference transduceroutput signals, electromechanical steering apparatus responds to bringthe torpedo into line with the target.

The pattern for one-half of a transducer is defined as a difference beamor a directivity pattern while the term, difference pattern, refers tothe signal pattern which is obtained when signals from transducer halvesare subtracted. The sum beam or sun pattern is the total transducersignal produced by adding the voltages generated by the individualtransducer elements.

in the past, homing systems have been proposed employing sum anddifference signals from directional transducers. One such transducersconsisted of a planar array of magnetostrictive elements arranged inpairs and stacked in columns. The transducer was geometric'ally dividedinto quadrants and had individual to each quadrant difference windingswound on the magnetostrictive elements to give quadrant directivitypattern signals which were fed to bridge circuitry. A sum signal forcomparison was provided by sum windings wound on each of themagnetostrictive elements in series circuit with each other but separatefrom the difference windings. The magnetostrictive elements of eachquadrant were shaded fromthe center to the outside of the transducerbyvarying the number of windings on each element. Final steering controlwas obtained by comparing phase shifted sum signals andv differencesignals to provide a steering signal which was proportional totheproduct of the magnitudes of the sum and difference voltages.

At least two problems have been present in the past with directivitytransducers of the type described. These problems are that of thetendency for false steering at target bearings other than that of asmall region near the center position of transducer halves and that oflarge sensitivity to noise sources at wide bearing angles. Because ofthe large phase angles involved as the bearing angle widens, falsesteering arises at relatively narrow target bearing angles.Theoretically the steering signal depends only on the difference inmagnitudes of the signals obtained from adding phase shifted sumvoltages and the difference voltages so that large differencevoltages atwide bearing angles should have only a noise effect on the homecircuitry. However, it being difficult to' maintain a precision balancein the homing circuitry, large difference voltages can cause thecircuitry to introduce phase or magnitude distortion which enhances anyill effects on steering signals. The theoretical limit for correctsteering is reached with transducers of the type considered as thebearing angle approaches 40, although experimentally false steeringoften occurred at angles as low as 18 for targets in the horizontalplane. A more satisfactory homing system which had a wider region ofcorrect steering and which had lower sensitivity to target signalsoutside of the steering region was therefore highly desirable.

The general purpose of this invention is to provide a underwaterdirectional homing transducer and method of shading the transducer whichembraces all the advantages of similarly employed transducers andpossesses none of the aforedescribed disadvantages. To attain this thepresent invention contemplates a. unique winding arrangement of thepick-up elements between the transducer quadrants whereby improvedsteering signalling is achieved.

An object of the present invention is to provide a signal processingsystem for a homing system wherein correct steering is maintained over awide bearing angle region and sensitivity to signals outside said regionis reduced.

Another object is the provision of a directional transducer whichdetects correctly the bearing of a target over a wide region and whichis relatively insensitive to sound sources at wide target angles.

Still another object is to provide a method of shading a sum anddifference signal generating transducer whereby false steering does notoccur at narrow target bearing angles and sensitivity of the transducerto sound sources at wide bearing angles is minimal.

Yet another object is the provision of a transducer having vibratorypick-up elements arranged in stacks in a planar array dividedgeometrically into quadrants which has low sensitivity to targets atangles where false crossovers associated with the sum pattern of thearray configuration can not be eliminated and which eliminatesoccurrence of false steerings at small target angles.

A further object is the provision of a transducer shading method forarranging the strengths of individual magnetostrictive stacks in a fourquadrant array of magnetostrictive elements to get distinct targetbearing information from a remote sound source.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings in which like referencesnumerals designate like parts throughout the figures thereof:

FIG. 1 illustrates a transducer winding arrangement for one quadrant ofa symmetrical directional transducer with references in the horizontaland vertical planes;

FIGS. 2a and 2b illustrate the transducer winding arrangement of FIG. 1for two quadrants with a reference in the diagonal plane;

FIG. 3a illustrates the geometrical arrangement of transducer quadrants;

FIG. 3b is a graphical representation of the vector addition andsubtraction of transducer signals from the quadrants of FIG. 3a;

FIG. 4 illustrates the geometry used in calculating directivity patternswith a phase reference point located at the center of a transducer;

FIG. 5 illustrates the transducer winding relationship of the presentinvention wherein the output of each quadrant shares with part of theoutput of each adjacent quadrant;

FIGS. 6a and 6b are graphs which illustrate bridge output voltages vs.bearing for a reference in the diagonal plane and horizontal or verticalplanes respectively;

FIGS. 7a and 7b are graphs which illustrate resulting receivingamplitude patterns of the quadrants as a function of target angle forquadrants having the winding arrangement of one embodiment of theinvention;

FIG. 8 is a graph illustrating steering signal voltage vs. target anglesfor right and left halves of a transducer with the shading arrangementof the invention; and

FIG. 9 illustrates the circuit relationship between a transducer and abridge in obtaining sum and difference signals.

Most of the structural design of the transducer of the present inventionis the same as those in the prior art similar to that disclosed by Blandet al. in U.S. Pat. No. 3,082,401 Mar. 19, 1963. The significantimprovement, however, is the novel shading arrangement and method ofobtaining same. FIGS. 1 and 2 show relative number of windings innon-normalized form which have been found to give satisfactorydirectional transducer shading. Before discussing FIGS. 1 and 2 indetail reference is first made to FIGS. 3 and 4 for a general discussionof torpedo homing system performance.

FIG. 3a shows the quadrants A, B, C and D of a transducer. Each of thequadrants have pick-up vibratory elements 4 such as the magnetostrictiveelements shown in the Bland et al. reference. The transducer of thepresent invention has pairs of these elements positioned at the relativepositions shown in FIGS. 1 and 2 with eight such pairs arranged in threecolumns in each quadrant. Complete symmetry of element size, spacing andmagnetostrictive strength is maintained among the quadrants.

With a target located at a bearing wider than zero, sound will impingeupon the elements lying nearest the sound source first and signalsgenerated by the transducer in the nearest quadrant or transducer halflead those of signals generated by the elements farther from the soundsource. If, for example, the target is in the horizontal plane thesignals from one-half of the transducer, quadrants A plus D in FIG. 3aare compared with signals from the other half, quadrants B plus C. FIG.3b shows, vectorially, signals from the transducer half, A and D,leading signals from the other half, B plus C, when a target is nearer Aand D. The homing system produces difference voltages by subtractingsignals from the transducer halves giving, for example, the vectorvoltages (A D) (B C) and (B C) (A D).

Because of the symmetry of the transducer halves, the differencevoltages for targets in the horizontal or vertical planes will always bein the 90 and 270 phase positions.

The homing system also produces a sum voltage (A D) (B C) which isalways in the horizontal or 0 and 180 phase positions. Some fraction forexample, A, of

the sum voltage is rotated in phase and added to the differencevoltages. If the rotation is clockwise the sum voltage increases the 270difference voltage and reduces the 90 difference voltage. At this pointany difference in magnitudes of these voltages results in a steeringsignal. Should a target lie dead ahead, (A D) is in phase with (B C) sothe difference signals between halves is zero and the steering signal ordifference between magnitudes of the rotated sum voltage added to thedifference voltages is also zero. If the target is moved in thehorizontal plane to the other side of the transducer (B and C), thevector position interchanges and the steering signal reverses from thatobtained in FIG. 3b. The same analysis can be applied to targets inplanes other than the horizontal except that signals from quadrants ineach half of the transducer will not be in phase. When the signals fromthe transducer halves pass 90 and 270, the sum voltage reverses polaritycausing false steering to result.

Considering now FIGS. 1 and 2 for one embodiment of the invention therelative number of windings per pair of vibratory elements is shown innon-normalized form for single quadrants and those elements adjacent thequadrants. Complete symmetry is assumed so that each of the quadrants iswound in the same manner. In FIG. 1 the references are the horizontaland vertical planes while in FIGS. 2a and 2b the reference is in a 45diagonal plane. The elements are separated a small distance (d) witheight pairs of magnetostrictive elements arranged in each quadrant asshown. The strength of elements are expressed as amplitude ratios whichindicate the number of turns on each element in columns Cn to Cm. Sincethe planar array of the transducer has circular symmetry the pattern ina plane containing the principal axis of the array and normal to thecolumns of the elements is identical to that produced by a line ofsegments whose strengths are the sums of the strengths of the elementsin each column. For reference waves in the plane shown in FIG. 1 thephase factor '11 represents the phase lag or lead of each elementreferenced to the central planes of the array, and target waves in the45 planes show the phase factor A representing the phase lag or lead ofeach element referenced in the central plane.

It was desired that nulls in the directivity patterns be obtained for:11 equal to 1r/2 and for A equal to 1r. Under these conditions it isfound that,

" "a "2 "4 equation where n n etc. if the total winding strength of theelements in the respective columns, and

N, N +N N1=Ng+ N N N equation (2) where N N etc. is the total windingstrength of the elements in the respective diagonal lines.

The geometry of FIG. 4, illustrates graphically a bottom view of onequadrant of the transducer elements represented in FIG. 1. All theelements in a column appear as a single element 5, 6, 7 to a sound raycoming from a bearing angle 0 along with a wave front of constant phaseperpendicular to the ray. When the center of the transducer is used as aphase reference point a phase angles for elements 12 and 1 1 can beshown to be 430 sin and 143 sin 0 respectively.

Referring again to FIGS. 1 and 2 the number of turns of winding on theelements were determined analytically based on the number of lines ofsegments existing in each plane being considered as well as the phaserelation of each line with respect to the reference. The elementstrengths of FIGS. 1 and 2 were obtained from the following mathematicalrelationships:

where: A= 1.122 rrsin 0 and R magnitude of resultant vectors as afunction of 0 applicable to the diagonal plane (two quadrants).Transducer 16 has four receiving circuits illustrated in FIG. bycircuits AE, BE, CE and DE. Each of the circuits form a series circuitwith windings on all the elements in a particular quadrant and withwindings on someof the elements in the two adjacent quadrants.

Output circuit AE from the transducer to bridge and steering circuithas. connected in series, windings L in quadrant A wound on all themagnetostrictive elements in section-A, windings L wound on one columnof magnetostrictive elements in quadrant D, and windings L wound on theelements of one column of quadrant B. Similarly, output circuit BE haswinding turns L L and L connected in series and wound on elements inquadrants B, C, A respectively; circuit CE has series connected windingsL L and L, wound on elements in quadrants C, B and D respectively; andoutput circuit DE is series wound on elements in quadrants D, A and Cwith windings L L and L respectively.

When signals are received by the bridge and steering circuit 15, eachsignal A, B, C or D indicates the signal pattern from its respectivequadrant, but the shading of some of the output from adjacent quadrantsresults in a wider region of correct steering and lower sensitivity atwide bearing angles. The four output signals are combined in any wellknown manner to provide the sum and difference signals for transducerhalves.

Bridge output voltages resulting from the transducer signals versustarget bearing for a reference wave front in the diagonal plane areshown in FIG. 6a. The patterns which determine azimuth and verticalsteering are given by:

ER=PRL+ (Q/ uma;

equation equation EL= PRL+ (Q/ M and equation equation where P e,, e ee,, or sum pattern;

P -j(e,, e e e or difference pattern for azimuth steering; and

P j(e,, e e e or difference pattern for vertical steering. The voltagese e e and e represent the voltages generated in their respectivequadrants by a sound wave impinging on the transducer. The voltage gainin the line shown in FIG. 3b is represented by Q in equations 5 to 8while N represents the step up turns ratio of a transformer (not shown)in the output circuitry. In FIG. 6a the ratio Q/N is assumed equal to5%.

FIG. 6a shows the up and down voltages E and E for the magnetostrictivewinding pattern shown in FIGS. 2a and 2b and also shows the sum voltageEs/2 for the special case where either E or B is equal to E and either Eor E is equal to E,,. The E and E signals cross at a target anglegreater than 60 but remain widely separated for angles less than 60. Itis noted at this point that the magnitude of the steering signal out ofthe bridge is proportional to the difference in magnitude of the E and Eor E and E signals. False steering therefore does not arise until theoutputs E and E cross, somewhere wider than 60.

False steering occurs in FIG. 6b at approximately 40 for targets in thevertical plane. In this case the left voltage E and right voltage E areequal to each other. The up and down bridge output voltages E and E donot cross over until an angle greater than 35 is reached. Thedifferences between E and E at target planes intermediate the I-I-V and45 planes produce results which indicate a gradual transition oftransducer characteristics between these planes.

Receiving patterns on the transducer having the winding strengths ofFIGS. 1 and 2 are illustrated in FIGS. 7a and 7b. FIG. 7b is thereceiving pattern for one quadrant representing the relative amplitudesof the resultant vectors obtained from the individual stacks ofmagnetostrictive elements of the transducer. FIG. 7b represents theamplitudes of two quadrants with the winding turns shown in FIGS. 2a and2b combined. The patterns of FIGS. 7a and 7b were obtained by solvingthe foregoing equations, Equation 3 and Equation 4 respectively.

Steering signals for the right and left halves of the transducer with atarget in the horizontal plane are shown in FIG. 8. Both halves reachmaximum sensitivity near the transducer center and correct steering isindicated up to the point of crossover, shown in the crosssectionalareas. The right half steering signal is correct to a bearing at 47 andthe half does not reach the false steering region until approximately313. It can also be seen in the cross-hatched region for both halvesthat sensitivity is considerably reduced at wide angles over that of theprior art devices without transducer shading which tends to balloonoutward into large signal lobes similar to that of the narrow anglelobes.

FIG. 9 shows a circuit used in obtaining sum and difference signals fromthe right and left and up and down halves of the transducer. The twoquadrants A and C have turns connected in a reverse manner to generate anegative voltage. Quadrants A, B; C and D are connected to the inputbridge points 21, 20, 22 and 23 respectively. Bridge outputs are takenfrom terminals 11-14 connected to resistors R,, R R and R respectively.The top and bottom outputs 11 (B A) and 13 (-C D) are used forhorizontal homing while the right and left outputs 12 and 14 (--A D andB C) provide vertical homing. The difference in voltage for the rightand left halves of the transducer therefore is (C D) less (B A) or (A D)(B +C). Similarly the voltage difference for the up and down halvesbecomes (A B) (C D). Transformers (not shown) in summer 25 are locatedbetween the transducer and bridge for reversing the polarity of signalsto obtain a sum signal. The sum signal is passed through phase shiftingmeans (phase shifter 28) to the four input points of the bridge to beadded to the difference signals. The final steering signal is thenproportional to the magnitude of the voltages.

From the foregoing it should now be evident that improved transducershading is provided which extends the region of correct torpedo steeringand which increases the probability of successful homing. The shading ofone quadrant by the provision of windings on adjacent quadrants enablesthe transducer of the invention to be less sensitive to wide anglebearing signals and is less likely to produce false steering signalsthan are transducers of the past.

The description of one embodiment is not intended to limit the inventionto the particular transducer described and obviously many other featuresand applications of the invention are contemplated. Ceramic pick-upelements might be substituted for the magnetostrictive elements andvarious stacking arrangements might be used. The specific number ofelements, the number of turns on each element, and the spacing betweenelements may be varied. Any appropriate means for combining the sum anddifference signals in obtaining steering signals may be used.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood, that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

l. A transducer for providing sum and difference signals to outputbridge circuitry comprising,

a plurality of stacks of vibratory elements disposed in a planar arrayof rows and columns symmetrically divided into quadrants, a firstelectrical output circuit, a second electrical output circuit, a thirdelectrical output circuit and a fourth electrical output circuitprovidin directivity patterns corresponding to firs secon third andfourth quadrants respectively,

each of said output circuits having first, second and third sets ofwindings connected in series, each of said first sets of windings woundon the element stacks of a corresponding quadrant, each of said secondsets of windings wound on a portion of the stacks in one adjacentquadrant, and each of said third sets of windings wound on a portion ofthe elements of the other adjacent quadrant.

2. The transducer of claim 1 wherein said vibratory elements aremagnetostrictive elements.

3. The transducer of claim 1 wherein said portion of element stacks inone adjacent quadrant is in the column adjacent to said correspondingquadrant and said portion in the other adjacent quadrant is in the rowadjacent to said corresponding quadrant.

4. The transducer of claim 3 wherein each quadrant contains eight stacksof magnetostrictive elements arranged, progressing from the transducercentral axis outward, to have three equispaced stacks of elements in afirst column, three equispaced stacks of elements in a second column,and two equispaced stacks of elements in a third column.

5. A homing system comprising the transducer of claim ll furthercomprising,

means connected to said output circuits vectorially summing saiddirectivity patterns into a sum signal for transducer halves,

means connected to the output of said summing means for phase shiftingsaid sum signal to be in phase with a transducer difference signal,

means connected to said transducer output circuits vectoriallysubtracting directivity patterns providing difference signals betweentransducer halves, and

means connected between said subtracting means and said phase shiftingmeans comparing said sum and difference signals and producing a steeringsignal output in response to a difference between said compared signals.

1. A transducer for providing sum and difference signals to outputbridge circuitry comprising, a plurality of stacks of vibratory elementsdisposed in a planar array of rows and columns symmetrically dividedinto quadrants, a first electrical output circuit, a second electricaloutput circuit, a third electrical output circuit and a fourthelectrical output circuit providing directivity patterns correspondingto first, second, third and fourth quadrants respectively, each of saidoutput circuits having first, second and third sets of windingsconnected in series, each of said first sets of windings wound on theelement stacks of a corresponding quadrant, each of said second sets ofwindings wound on a portion of the stacks in one adjacent quadrant, andeach of said third sets of windings wound on a portion of the elementsof the other adjacent quadrant.
 2. The transducer of claim 1 whereinsaid vibratory elements are magnetostrictive elements.
 3. The transducerof claim 1 wherein said portion of element stacks in one adjacentquadrant is in the column adjacent to said corresponding quadrant andsaid portion in the other adjacent quadrant is in the row adjacent tosaid corresponding quadrant.
 4. The transducer of claim 3 wherein eachquadrant contains eight stacks of magnetostrictive elements arranged,progressing from the transducer central axis outward, to have threeequispaced stacks of elements in a first column, three equispaced stacksof elements in a second column, and two equispaced stacks of elements ina third column.
 5. A homing system comprising the transducer of claim 1further comprising, means connected to said output circuits vectoriallysumming said directivity patterns into a sum signal for transducerhalves, means connected to the output of said summing means for phaseshifting said sum signal to be in phase with a transducer differencesIgnal, means connected to said transducer output circuits vectoriallysubtracting directivity patterns providing difference signals betweentransducer halves, and means connected between said subtracting meansand said phase shifting means comparing said sum and difference signalsand producing a steering signal output in response to a differencebetween said compared signals.